You know you need a holiday when:
1. You are getting through work faster than you thought, so you go and ask your supervisor for more.
2. In a lecture/seminar, you drift off and spend five minutes looking around the room wondering what animal each person would be. (The lecturer: a shaggy dog.)
3. You hear a history in-joke like "What? We don't have to look at primary sources at postgrad level, do we?" and fall about hysterically laughing.
4. On a similar vein, you start collecting historical insults: eg "I can see you haven't read Foucault."
5. You start fantasising about being able to ignore all other essays/seminars/assignments and just hunker down somewhere working on your thesis day-in, day-out.